It has heretofore been established that many material characteristics of polyethylene terephthalate (PET) are improved by high biaxial molecular orientation of the plastic during blow-molding, particularly when manufacturing containers for packaging contents under pressure, such as disclosed in U.S. Pat. No. 3,733,309. In practice, the injection-molded preform design is such that molecular orientation may take place in both axes of the container by holding the preform in a mold cavity having the volumetric configuration of the desired article, stretching the preform longitudinally within the mold and expanding the preform transversely with high pressure air into the final shape of the article and mold cavity.
Prior container designs of biaxial molecular oriented PET, particularly for carbonated beverages, utilize a free-standing highly oriented base design which purportedly lends strength and rigidity necessary to withstand elevated pressures. The methodology for formation of freestanding pressure-resisting bases for these types of PET biaxial molecular oriented containers is described in U.S. Pat. No. 3,598,270 for a "petaloid" type base and in U.S. Pat. No. 4,465,199 for a "champagne" type base. However, both of these types of bases in a stretch blow-molded PET container are difficult to form, since they require high blowing pressures and/or secondary mold motions in order to stretch and blow the PET material into tight and highly defined annular spaces.
It has also been determined, in wide-mouth stretch blow-molded PET containers, that it is desirable to have a high biaxial molecular oriented flange of desired strength and thickness extending radially outwardly from around the wide open mouth for receiving a metal end closure by conventional double seaming operations to close the stretch blowmolded PET container with pressurized contents, such as tennis balls, therein. Such a stretch blow-molded widemouth PET flanged container is disclosed in U.S. Pat. Nos. 4,496,064 and 4,567,843 which is described as requiring complete biaxial molecular orientation for adequate performance. The method described in these patent discloses the formation of an intermediate article utilizing an oblique truncated cone type of accommodation area, including the flange portion surrounding the wide open mouth of the tubular body, which imparts a gradual increase in biaxial molecular orientation from a neck area at the top to the flange portion at the bottom of the accommodation portion. The accommodation portion is then removed by cutting through the flange to provide a container having a flange around the open mouth with biaxial molecular orientation. However, the design of the accommodation portion in the form of the oblique truncated cone makes it difficult to consistently control the degree of biaxial molecular orientation and the thickness of the flange material which often results in undesirable strength and thickness in the flange for receiving a metal end closure by double seaming operations.